Auto merge of #130337 - BoxyUwU:anon_const_macro_call, r=camelid

Fix anon const def-creation when macros are involved take 2

Fixes #130321

There were two cases that #129137 did not handle correctly:

- Given a const argument `Foo<{ bar!() }>` in which `bar!()` expands to `N`, we would visit the anon const and then visit the `{ bar() }` expression instead of visiting the macro call. This meant that we would build a def for the anon const as `{ bar!() }` is not a trivial const argument as `bar!()` is not a path.
- Given a const argument `Foo<{ bar!() }>` is which `bar!()` expands to `{ qux!() }` in which `qux!()` expands to `N`, it should not be considered a trivial const argument as `{{ N }}` has two pairs of braces.  If we only looked at `qux`'s expansion it would *look* like a trivial const argument even though it is not. We have to track whether we have "unwrapped" a brace already when recursing into the expansions of `bar`/`qux`/any macro

r? `@camelid`

Author: bors